TOKYO, June 2 -- North Korea's ailing leader has chosen his youngest son as heir to the family dynasty that rules the secretive state, South Korea's intelligence service told lawmakers in Seoul.

Kim Jong Un, 26, who attended a Swiss boarding school and reportedly admires basketball great Michael Jordan, is the third son of Kim Jong Il, the "Dear Leader" who suffered a stroke last summer and who has since appeared thin and frail. He is the grandson of the late Kim Il Sung, the "Great Leader" and founding dictator of North Korea.

If Kim Jong Un does become the new leader -- and there are analysts who doubt the decision is final -- this second consecutive father-to-son handoff would be unique among nations that call themselves communist. There was no indication, however, that Kim Jong Il would be handing over power anytime soon.

Kim Jong Un attended the International School of Berne, which is about 15 minutes from the Swiss capital and a few hundred yards from the North Korean Embassy. While Kim was at the English-language school, which has about 280 students from 40 countries, he befriended the children of American diplomats and learned French and German, according to the Swiss weekly L'Hebdo.

Kim attended the school under the false name of Pak Chol, the weekly said, and school officials and his classmates "thought they were dealing with the son of the driver of the embassy." Friends and staff at the school remembered a shy boy who enjoyed skiing, loved the National Basketball Association and spoke highly of action-movie actor Jean-Claude Van Damme. He reportedly left the school at age 15 to return to North Korea, and little about his life there is known to the outside world.

Link to Military Tension

The younger Kim's name surfaced about four months ago as his father's likely successor, but it wasn't until after last week's underground nuclear test in the North that Kim Jong Il informed top officials in Pyongyang and diplomats in foreign missions that Jong Un would be his successor, intelligence officials told members of the National Assembly in Seoul.

South Korea's National Intelligence Service declined to confirm the reports. But one of the lawmakers, Hong Jung-wook, a member of the ruling Grand National Party, said intelligence officials think the recent spike in military and political tension on the Korean Peninsula is closely related to the transition underway in Pyongyang. He said in an interview that the South Korean government has created a "special team" to analyze the succession.

"Kim Jong Un is very young, too young for a smooth transition to power," Hong said. "He seems to need support from the military and seems to be conforming to military preferences in his policy direction. We could interpret the recent developments -- the testing of a nuclear bomb and the testing of missiles -- as a way to consolidate power for the military and for Kim Jong Il's successor."

Kim Jong Il has asked officials in North Korea and diplomats overseas to pledge loyalty to his son, according to a statement issued Tuesday by Park Jie-won, a member of the National Assembly who serves on its intelligence committee.

New Songs, Slogans

Schoolchildren in Pyongyang have already begun singing the praises of Kim Jong Un, according to a report from Rescue the North Korean People, a relief group in Osaka, Japan, that has informants inside North Korea.

"That fact that schools are teaching students to sing such songs is tantamount to officially declaring the heir," the report said. "Elementary school children on a street corner in Pyongyang are singing a song about Gen. Kim Jong Un. They said they sing this song all day without doing any other regular classes."

Soldiers, too, are shouting new slogans, including "With all our hearts, let's protect Kim Jong Un, the young general, the morning star general who inherits the bloodline of Paektu," the report said.

Snow-covered Mount Paektu is the highest peak on the Korean Peninsula and a revered place. North Korea claims that Kim Il Sung organized guerrillas to fight Japanese occupation from bases on the mountain and that Kim Jong Il was born there. But records show that the communist resistance and the Dear Leader were born in what was then the Soviet Union.

It has been state policy in North Korea since the 1950s to create cults of personality around the Kim family. Kim Il Sung and Kim Jong Il were ascribed godlike powers and unlimited knowledge. The practice has been supported by relentless propaganda that dominates school curriculums and by strict government control over access to foreign media or any outside information.

Kim Jong Un is the second son of Kim Jong Il's third wife, Ko Yong Hi, who died five years ago of breast cancer at age 51. At 26, he is seven years younger than his father was when he was designated as the future leader. Kim Jong Il got the nod in 1974, two decades before the death of his father.

Analysts had expected Kim Jong Il to name a successor in 2012, the centenary of the birth of his father. But his health appears to be failing. In recent video clips he has looked gaunt, tired and much older than his 67 years.

He has two other sons. But the eldest, Jong Nam, 38, lost favor in 2001 when he was caught trying to enter Japan on a phony passport. He told Japanese officials he wanted to visit Disneyland in Tokyo.

The middle son, Jong Chol, 28, was regarded by his father as unfit for leadership and too feminine, according to Kenji Fujimoto, a former Japanese sushi chef for the North Korean leader and author of the memoir "I was Kim Jong Il's Cook."

Special correspondents Stella Kim in Seoul and Akiko Yamamoto in Tokyo contributed to this report.